In drilling offshore wells, a single drilling platform is typically positioned at a central location and a plurality of wells are successively drilled in various radial directions. To direct these wells outwardly from the central platform it is, of course, essential that substantial portions of these boreholes be drilled along nearly-horizontal axes in order to reach their respective targets. It will be appreciated, therefore, that it is all but impossible to lower cable-suspended well tools to the bottom of such highly-deviated wells.
Accordingly, to move cable-suspended tools into these deviated intervals, a common operating practice is to couple the tools without a suspension cable to the lower end of a joint of drill pipe and progressively push the tools into the well bore as the string of drill pipe is successively assembled at the surface and lowered into the well bore. At some time during the assembly of the drill string, a special latching sub or a so-called "wet connect" device is coupled to the free end of the tool suspension cable and introduced into the drill string by way of a so-called "side entry" sub that is coupled into the drill string before additional joints of drill pipe are coupled thereto. Although it is not essential that the wet connect device be immediately mated with a companion device on the upper end of the well tools, this connection is typically made so that the suspension cable will be electrically connected to the well tools as they are lowered on into the well bore.
It will be appreciated that once the cable has been connected to the well tools and the tools have reached the bottom of the well bore, the tools are in readiness to be operated as needed for carrying out their intended operations. For instance, when one or more logging tools are coupled to the lower end of the drill string, the logging tools will progressively log the open borehole below the casing string by alternately raising the drill string and removing successive stands of the drill pipe from the upper end of the drill string. Once the side entry sub is brought to the surface, the wet connect device is disconnected and the cable is removed.
Those skilled in the art recognize that some logging tools include a wall-engaging member which must be positioned firmly against the borehole wall in order for the logging tool to operate properly. Similarly, other types of logging tools employ extendible wall-engaging members which must be moved outwardly into engagement with a borehole wall. Nevertheless, if one of the latter logging tools is oriented in a substantially-inclined interval of a borehole so that the wall-engaging member is facing downwardly, the weight of the tool string will prevent the member from been extended outwardly as necessary for the tool to operate in that interval of the borehole. Regardless of the type of wall-engaging member employed, it will be recognized that there has been no practical way heretofore for reliably positioning one of these tools in a selected orientation as it is passed through a highly-deviated borehole interval.